1. Field of the Invention
The present invention relates to a method and to an arrangement for extracting an auxiliary data clock from the clock and/or the clock phase of a synchronous or plesiochronic digital signal.
2. Description of the Prior Art
From the incoming digital signals at the inputs of devices for transmitting or processing digital signals, their clock must be recovered. A corresponding clock recovery facility TR is disclosed, for example, as a block in FIG. 4 of the periodical "telecom report", Vol. 9, No. 3, 1986, pp. 190-197.
The clock frequency of the plesiochronic digital signals correspond to a nominal value, with a slight relative deviation, the permissible maximum value of which is typically of the order of magnitude of a few times 10.sup.-5. As far as can be technically implemented, the clock frequency of synchronous signals in the mean corresponds accurately to a nominal value. Interfering influences in electric circuits and on the transmission path have the effect that the instantaneous frequency of synchronous signals also slightly deviates from the nominal value. Therefore, there is no significant difference between the two types of signals with regard to the problem of clock recovery. Therefore, the illustrative embodiments of the present invention are restricted to plesiochronic signals.